Many patients, in particular those suffering from respiratory diseases, are unable to cough for themselves, and require the assistance of a machine which can provide a series of positive and negative pressure cycles, alternately forcing air into the patient's lungs and allowing air to flow out of the patient's lungs. (The term “positive pressure” is used herein to mean a pressure above the ambient atmospheric pressure, and the term “negative pressure” is used to mean a pressure below the ambient atmospheric pressure).
The lungs and bronchial passageways of a person suffering from respiratory disease will usually continue to secrete fluids to keep the bronchial tract moist, as in a healthy person, although in some patients the secretion of fluids may increase as a symptom of the respiratory disease. If the bronchial secretions are allowed to remain in the lungs or bronchial passageways they can impair the lung function and/or harbour germs, and can ultimately cause the death of the patient.
A healthy person is able to cough in order to remove any build-up of bronchial secretions, the cough function forcing air out of the person's lungs at significant force, the moving air also expelling or at least releasing any bronchial secretions which have built up.
A patient suffering from respiratory disease, however, will often not have sufficient cough function, i.e. even if the patient retains the stimulus to cough he or she will not be able to generate sufficient force to cough effectively so as to expel or release any built-up bronchial secretions. Alternative means must therefore be provided to remove the patient's bronchial secretions.
Conventional ventilators which are adapted to assist the breathing of a patient are not able to replicate the cough function.
Physiotherapy is a known treatment to assist the removal of bronchial secretions, the bronchial secretions being released from the lungs of the patient by physical force appropriately applied by a trained person. However, many patients suffering from respiratory disease are treated in the home, and a trained person is not always available to administer the required physiotherapy.
Some ventilators have been modified to provide a “cough programme” which seeks to replicate the cough function in a patient. The cough programme operates by rapidly switching from positive to negative pressure (corresponding to inspiration of the patient and exsufflation of the patient respectively), the output of the pump being varied to control the inspiration and exsufflation pressures. These ventilators suffer from the major drawback that the inspiration pressure and exsufflation pressure cannot be controlled independently. Another major drawback is that the inspiration and exsufflation pressures cannot be altered rapidly, as is often required during ventilation. For example, the patient's face mask may move during the cough programme so that more (or less) of the air being delivered from (or drawn into) the ventilator is passing into (or out from) the patient's lungs.
It is therefore desired to provide a treatment device which can replicate the cough function and which can be used in a person's home without necessarily requiring the assistance of a trained person, and which avoids or reduces the drawbacks of the above-described modified ventilators.